A diffusion bonding method has been known as one of the methods for bonding metallic materials. When bonding metals by this method, because the surface roughness of materials to be bonded significantly affects the joint efficiency, the ends of the materials are generally cut or ground to achieve a desired roughness before the materials are set in the diffusion bonding apparatus for diffusion bonding.
In this general procedure, materials to be bonded are set in a diffusion bonding apparatus without adjusting the ends of the materials to face parallel to each other, assuming that a proper contact is obtained at the ends of the material to be bonded by creep caused by pressure and heat applied thereto prior to bonding.
However, a study made by the inventors of the present invention has discovered that when bonding tubes or pipes by this generally employed method of diffusion bonding, joint efficiency drops because some parts may not contact each other under a desired pressure depending on a certain degree of parallel of materials to be bonded.
Therefore, when bonding tubes or pipes through this generally employed diffusion bonding method, it is essential to adjust the ends of the materials to be bonded to face parallel to each other before setting the materials in a diffusion bonding apparatus. However, because most pieces of tube or pipe to be bonded are long, the adjustment is troublesome and time-consuming.
However, most products manufactured by diffusion bonding are relatively small, and it is impossible to employ a prior art diffusion bonding apparatus in the manufacture of extensively long pieces such as oil-well pipes which extend several kilometers.
Therefore, the arrival of a diffusion bonding apparatus suitable to the manufacture of extensively long pieces is much awaited by manufacturers of extensively long pipes such as oil-well pipes.
Another problem of a prior art diffusion bonding apparatus is that when bonding metallic materials by the prior art diffusion bonding apparatus, a difference may occur in the joint of the two materials as shown in FIG. 46(a). Marks T1 and T2 in FIG. 46 represent materials which are bonded.
Subsequently, when a difference occurs, it remarkably weakens the strength, especially the fatigue strength, of the joint. Consequently, when such a difference occurs, it is usually corrected by forming a taper a and b at the joint, as shown in FIG. 46(b), by applying cutting or grinding finishing thereto.
However, correction in such a way may lead to a drop in the work efficiency at diffusion bonding since the correction work is troublesome, because the work is carried out for a materials which becomes much longer after being bonded.
Furthermore, induction heating has usually used a heating coil c as shown in FIG. 47 in which the material T to be heated is inserted, heated and then pulled out.
However, when heating an extensively long piece such as a pipe, insertion and extraction of the material T in and out of the heating coil c takes much time because of its long length, thus impairing the productivity.
Furthermore, in diffusion bonding, it is the conventionally employed method that a bonding part j is covered with a gas jacket d as shown in FIG. 48 in order to prevent the oxidation of the bonding part j. Because of a gap created between the gas jacket d and materials T and T, inert gas (herein after called shielding gas) is supplied to the gas jacket d from a nozzle e to prevent air from going into the gas jacket d, and the bonding part j is bonded while being shielded. In other words, with the shielding gas leaking out of the gap between the gas jacket d and the materials T and T, air is prevented from going into the gas jacket d while materials are being bonded. In FIG. 48, the mark c represents a high frequency heating coil.
However, when the materials are bonded while letting the shielding gas go out in the above manner, it creates a flow of gas inside the gas jacket d cooling the circumference of the bonding part j. As a result, the bonding part is not sufficiently heated causing unsatisfactory quality and strength in joints.
The present invention is made to resolve the above-mentioned disadvantages of the prior arts.
Namely, it is an object of the present invention to provide a diffusion bonding method and a diffusion bonding apparatus that will facilitate the setting of the materials in a diffusion bonding apparatus when bonding long pieces of tubes or pipes.
It is another object of the present invention to provide a diffusion bonding apparatus which is applied to manufacture of extensively long pipes such as oil-well pipes which extend several kilometers.
It is another object of the present invention to provide a method and an appratus for adjusting position of materials to be bonded by diffusion bonding so that a difference in the joint is prevented.
It is another object of the present invention to provide a heating coil to heat speedily an extensively long piece such as a pipe.
It is another object of the present invention to provide a shielding device and the shielding method for a bonding part in diffusion bonding which do not cause the degradation in quality and strength in joints.